dt-bindings: input: add qpnp-power-on bindings

Add device tree bindings for Qualcomm Technologies, Inc. QPNP
Power-on devices.  These are PMIC peripherals which manage PMIC
power on, power off, key presses, and other related activities.

This snapshot is taken as of msm-4.19
commit 47598dd0e809 ("input: misc: qpnp-power-on: add support
to power off a modem chip").

Change-Id: If5e727c812a3c8cdcc263a40c72de50bb3ffbc78
Signed-off-by: David Collins <collinsd@codeaurora.org>